There have been many proposals in the literature for such compositions. In general they comprise a viscous or solid radiation-curable ethylenically unsaturated macromolecular or resinous, e.g. oligomer or polymer component dissolved or dispersed in a liquid diluent comprising one or more ethylenically unsaturated monomers which are capable of copolymerising with the said component.
To be commercially acceptable as an adhesive for bonding glass in large scale manufacturing operations such as the manufacture of laminated glass products, the compositions must not only bond adequately in the cured state to the glass and to the other substrate, which may or may not be glass, but must also have an adequate shelf life and yet be able to be cured rapidly when exposed to the chosen irradiation, and must be available in a form having a viscosity sufficiently low in the uncured state to permit its facile application to a substrate in a thin and uniform layer without the need for sophisticated equipment.
For the production of laminated glass products intended to be used as windows or doors or in vehicles, the cured product from the composition must also be clear, colourless and transparent, preferably have a refractive index at least close to that of glass, exhibit adequate water- or moisture-resistance and be resistant to aging in sunlight. Further, since for many intended end uses it is desirable that at least one of the layers of the laminate is an organic glass such as methacrylate or polycarbonate or that a plastics foil such as of vinyl chloride polymer be provided between two glass sheets (one or both of which may be of organic glass), it is also desirable for the composition to bond well to certain plastics materials, especially those that are available as transparent sheets or film.
Much effort has been expended over the last 10-15 years in developing suitable compositions and a very wide variety of resinous components and diluent compositions has been proposed in the literature. One group of resins that has attracted particular interest comprises those which contain urethane groups in an oligomer or polymer chain and particular examples of these are the compounds obtainable by reacting a polyol with a polyisocyanate to form a urethane intermediate having terminal hydroxy and/or isocyanate groups and reacting the intermediate with an .alpha..beta.-ethylenically unsaturated compound having a group which is reactive with a hydroxy or isocyanate group as appropriate. Where the unsaturated compound contains a carboxylic group attached to a carbon atom of the .alpha..beta.ethylenically unsaturated group, i.e., contains the group ##STR1## the product, which will usually be oligomeric, is called, for ease of reference, a urethane acrylate.
One class of composition that has shown particular promise as an adhesive for glass contains a urethane acrylate as the resinous component and a reactive diluent such as acrylic acid, e.g. as described in European patent publication No. 10355. However, an improvement in the bond obtained between glass and plastics materials, especially vinyl chloride polymers, using the composition would be desirable. In the production of glass laminates, two properties of the bond which are important are the adhesive or bond strength, e.g. as measured in a Peel Test, and the performance of the bond under impact. The latter can be gauged from the performance of the bond in the Peel Test. If the force required when performing the Peel Test at a steady parting rate of e.g. 30 cm/minute is not uniform and/or if it drops markedly if the parting rate is increased sharply, e.g. as when the components are pulled apart sharply by hand, the bond is said to exhibit "driness" and is less likely to perform well under impact; in particular, delamination and/or splintering of the glass may occur. It is in these properties of bond strength and driness in particular where improvement is desired; i.e. an increase in bond strength and/or a reduction in "driness" which can alternatively be described as an increase in the "softness" of the bond. Of course, such improvement should be obtained without unacceptable deterioration of other properties, particularly clarity, colour, reactivity, water-resistance and resistance to ultra-violet light. To improve the bond, without significant loss of water-resistance in particular, however, presents a problem because these properties conflict. Adhesion to glass requires a degree of hydrophilicity whereas hydrophobicity is required for water resistance.